I appreciate the replies and the debating was very interesting. To re-cap, we are trying to see if we can come up with a simple way to calculate the temperature rise in a connector at different current levels if we already know that the temperature rise is 30ºC at the rated current (which is how most connectors are rated).
We know the calculated results would be just an estimate and we are making the assumption that the power dissipation and thermal resistance would stay fairly constant in the temperature range that we want to calculate. I took John's advice and decided to do some measurements just to see if the results would track our I^2 presumption. I took a standard Molex connector (single) pin and socket rated 19 amps (this is NOT the 50 amp connector from my original email) and soldered them onto 16 AWG wire and mounted them in free space and connected the wires to my Ground Bond Tester (constant current source). I stuck a thermocouple with thermal paste into the connector pin as close to the junction as possible. Passing current through the connector pins gave me the following results: 5A = 2.5ºC rise over ambient 10A = 11ºC rise 15A = 22ºC rise 20A = 44ºC rise So it would seem that in this case our assumption was pretty close if not right on. Doubling the current gave us approximately a 4X change in our temperature rise. We'll have to do more real world measurements to see if the results are similar with other connectors. Thanks for everyone's help. The Other Brian From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of John Woodgate Sent: Sunday, March 08, 2009 5:21 PM To: john...@itesafety.com Cc: emc-p...@ieee.org Subject: Re: De-Rating internal Connectors for Temperature In message <49b42f6e.3030...@itesafety.com>, dated Sun, 8 Mar 2009, Robert Johnson <john...@itesafety.com> writes: >Temperature is not proportional to current or current squared or >power.. >Temperature rise is not proportional to current or current squared or >power. >These formulas were all pure guesses. Not in my case: I explained its approximate nature. >Temperature is proportional to kinetic energy (more or less). Power is energy per unit time. If power is constant, whatever is proportional to energy is proportional to power. >You need to go back to the physics and figure out where the energy is >going and how the energy relates to the temperature of a substance. It >turns out to be a very complicated subject (eg). You can make anything complicated. The genius is in making it simple. > >A second major flaw here is a misunderstanding about temperature >manipulation. >You can double the temperature of a product from 1°C to 2°C. You can >also double the temperature of a product from 50°C to 100°C. You can >increase the temperature of a product a million fold to 1°C (from >.000001°C). You have to be really careful if you are manipulating >temperatures without using an absolute scale. If you are trying to >relate something to a fraction of the temperature scale (like Celsius >or Fahrenheit) you can quickly get into trouble. I made it clear that the connector problem is a matter of temperature RISE, not temperature on a scale. Others may have considered temperatures on a scale; that is indeed very liable to cause errors. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk Things can always get better. But that's not the only option. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@ptcnh.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@ptcnh.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
